This invention relates to a fuel cell using a liquid electrolyte, i.e. an electrolyte-type fuel cell, having a suitable system for supplying a liquid electrolyte to the fuel cell, and particularly to a phosphoric acid-type fuel cell using phosphoric acid as an electrolyte.
In an electrolyte-type fuel cell which comprises at least one unit cell comprising a porous matrix impregnated with a given amount of a liquid electrolyte and a pair of a fuel electrodes and an air electrode, provided on one side and another side of the matrix, respectively, the impregnated liquid electrolyte is lost with increasing operating time due to its evaporation, etc., and the performance of the fuel cell is gradually deteriorated. Thus, it is necessary to supplement the matrix with the liquid electrolyte.
Heretofore, the following systems for supplementing the matrix with a liquid electrolyte, particularly liquid phosphoric acid, have been proposed.
Japanese Patent Application Kokai (Laid-open) No. 59-60973 discloses a system for supplying liquid phosphoric acid mist to a fuel gas supply line, and then supplying a mixture of fuel gas and the liquid electrolyte mist to a fuel electrode, thereby supplying the liquid electrolyte to the matrix, but fails to disclose a specific means for supplementing the matrix with the thus supplied liquid electrolyte.
Japanese Patent Application Kokai (Laid-open) No. 60-121680 discloses a fuel electrode provided with such pores or water non-repellent parts that can pass liquid phosphoric acid electrolyte mist to the matrix, and particularly a system for supplying 70-85 wt. % phosphoric acid mist together with a fuel gas to the matrix through the fuel gas grooves and the pores or water non-repellent parts of the fuel electrode layer while the fuel cell power generation is discontinued.
Japanese Patent Application Kokai (Laid-open) No. 60-151977 discloses a system for atomizing a liquid phosphoric acid electrolyte with a portion of fuel gas and supplying the atomized electrolyte, together with the fuel gas, to the matrix through a large number of pores provided through a fuel electrode.
Japanese Patent Application Kokai (Laid-open) No. 60-218770 discloses a system for injecting a liquid phosphoric acid electrolyte towards gas passage grooves in a stack of unit cells through an injecting nozzle provided at the side wall of the stack, thereby supplementing the matrix with the liquid phosphoric acid electrolyte through pores or hydrophilic (water nonrepellent) parts provided through the electrode layer, but it is difficult to efficiently inject the liquid phosphoric acid electrolyte into the grooves, and most of the liquid electrolyte deposits on the side wall of the stack and flows down along the side wall of the stack That is, it is difficult to uniformly supply the liquid electrolyte to the unit cells in this system. This is because the ratio of the opening area of the total grooves to the side wall area of the stack is very small, for example, about 10 to about 15:100.
Japanese Patent Application Kokai (Laid-open) No. 61-42870 discloses a system of supplying phosphoric acid electrolyte vapor to a fuel cell, as mixed with a gas to a fuel cell, recovering phosphoric acid from the effluent gas and recycling the recovered phosphoric acid.
Though the foregoing prior art discloses systems for supplying phosphoric acid electrolyte mist or vapor, together with a fuel gas, to gas flow passage grooves in the fuel electrode and supplementing the matrix with the electrolyte through pores or water nonrepellent parts provided in the fuel electrode, the particle size of liquid electrolyte mist (which will be hereinafter referred to as "mist sizes") and the system for trapping the liquid electrolyte mists are not taken into account at all in any of the foregoing prior art. When the mist size is larger, most of the mists deposits on the inside wall of a piping or manifold to the fuel cell stack or the side wall of the fuel cell stack, and it is difficult to supply the electrolyte to the fuel cell. When the mist size is smaller on the other hand, most of the mist passes through the gas flow passage of the fuel cell, and it is also difficult to supplement the matrix of the fuel cell with the liquid electrolyte.
That is, no consideration is given to the mist size and the system for trapping the electrolyte mist in any of the foregoing prior art, and there have been such problems as a poor mist trapping efficiency, deposition of liquid phosphoric acid electrolyte mist onto deposition-unwanted positions, and occurrence of short circuit on the stack side wall or corrosion of structural members due to the deposition of the liquid electrolyte mist.